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O: Fachverband Oberflächenphysik

O 11: Focus Session: Spins on Surfaces studied by Atomic Scale Spectroscopies II

O 11.2: Vortrag

Montag, 18. März 2024, 15:30–15:45, MA 004

Theory of a Single Magnetic Impurity on a Thin Metal Film in Proximity to a Superconductor — •Jon Ortuzar Andres¹, Stefano Trivini¹, Katerina Vaxevani¹, Jingchen Li², F. Sebastian Bergeret^3,4, Miguel A. Cazalilla^4,5, and Jose Ignacio Pascual^1,5 — ¹CIC nanoGUNE, Donostia-San Sebastián, Spain — ²School of Physics, Sun Yat-sen University, Guangzhou 510275, China — ³Centro de Física de Materiales (CFM-MPC) Centro Mixto CSIC-UPV/EHU, Donostia-San Sebastián, Spain — ⁴Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain — ⁵Ikerbasque, Basque Foundation for Science, Bilbao, Spain

Magnetic impurities on proximitized thin films can host Yu-Shiba-Rusinov states, entangled excitation between the spin of the impurity and the electrons of the substrate. We argue that the formation of YSR excitations in proximitized thin films is largely mediated by a type of Andreev-bound state named after de Gennes and Saint-James. This is shown by studying an experimentally motivated model and computing the overlap of the wave functions of these two sub-gap states. We find the overlap stays close to unity even as the system moves away from weak coupling across the parity-changing quantum phase transition. Based on this observation, we introduce a single-site model of the bound state coupled to a quantum spin. This model can qualitatively explain the complex behaviour of magnetic impurities interacting with the proximitized metal. The adequacy of this description is assessed by reintroducing the coupling to the continuum as a weak perturbation within the framework of Anderson's poor-man's scaling.

Keywords: Superconducting Proximity Effect; Yu-Shiba-Rusinov; Single-Site Model